Is centrifugal force false?

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Is centrifugal force false?

Postby gsalih on July 9th, 2011, 8:38 am 

Is centrifugal force a false force?
Because if one swings a can in a circle
and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.
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Re: Is centrifugal force false?

Postby CanadysPeak on July 9th, 2011, 7:13 pm 

gsalih wrote:Is centrifugal force a false force?
Because if one swings a can in a circle
and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.


Perhaps not "false" but fictitious because it only seems to exist.

For this one, Wiki is a good start.

http://en.wikipedia.org/wiki/Fictitious_force
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Re: Is centrifugal force false?

Postby farplaces on July 12th, 2011, 8:24 pm 

So then, fill that can with water and then swing it in a circle and you will have an example of centrifical force as the water rushes to the inner can perimeter in true balance of its own consistancy.
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Re: Is centrifugal force false?

Postby Yoron on July 16th, 2011, 3:20 pm 

It's a force, moving something outward, as defined from you. But think of the universe, if it was to swing something around, to what should that force be defined to? If the universe is all there is?
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Re: Is centrifugal force false?

Postby Natural ChemE on July 18th, 2011, 5:31 pm 

gsalih wrote:Is centrifugal force a false force?
Because if one swings a can in a circle and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.


As CanadysPeak pointed out, centrifugal force is a fictitious force.

The question that you asked almost makes me think that someone's been messing with you since there's misdirection embedded in the question itself. So let's sort this out.

Say you're standing still on a spot in your office, or wherever. You're holding a bucket of water and spinning around. There are two reference frames most people would try to view you from. First, they could view you from the reference frame of the ground - presumably an inertial reference frame. Second, they could view you from the reference frame where you and the bucket are stationary but the ground is spinning under you.

Newton, the dude who came up with a lot of Classical Physics, would've preferred the first reference frame. Since it's an inertial frame, you don't have centrifugal force. Everything is already described without it. I mean, sure, you still feel the bucket stretching out the arm that's holding it, but that's not centrifugal force. Rather, the stretchy feeling in your arms is you pulling the bucket. By pulling the bucket, you keep changing its flight path from what would be a straight tangent line (like you see when you let go) to the circular flight path (like you see when you keep holding on).

Okay, stop and clear everything. We're moving to the second perspective now and the stuff that we just said doesn't apply to this one.

Here in the second reference frame, you and the bucket and holding still while the ground below you is rotating. Of course, you still feel your arm holding the bucket being stretched. Now it's centrifugal force pulling the bucket away and tension giving your arm the stretchy feeling. See, you're not pulling the bucket in this frame since you're both still. Rather, it's centrifugal force that gives your arms the stretchy feeling. What happens if you let go? The centrifugal force pulls the bucket directly away from you in a straight line, just like you expected. At least initially. The motion after that initial moment gets more complicated.

So why was there centrifugal force in the second example but not the first? Well, the most common way to see it is this. We do Physics in inertial reference frames, like the first one and not like the second one. When we do Physics to non-inertial frames, we have to take special considerations into account - considerations like centrifugal force and the other fictitious forces.

And why did I say that there’s misdirection embedded in your question? When you say
Because if one swings a can in a circle and releases it at the exact position, the centrifugal force should carry it directly to the right.
, I’m not exactly sure what you mean, but it’s obvious that you’re talking about the second reference frame since you refer to centrifugal force. However, when you then ask the question
But in real life, it does not, it travels tangent to the circle in which it was swinging.
, this observation concerns the first reference frame where you’re spinning and there is no centrifugal force. In short, the question mixes up the reference frames.

So, intentional or not, it’s kind of a trick question. =P

PS- Sorry that this was so long and wordy. I'm honestly not sure what's wrong with me today.
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Re: Is centrifugal force false?

Postby Yoron on July 20th, 2011, 6:11 am 

Nice explanation.

I've always found the centrifugal/centripetal force confusing myself. Reading you I see the definition 'inertial frame' which made me think of inertia. Couldn't you define it as it is the inertia of that can acting on you, giving you the feel of it 'pulling' at you instead? Anything moving in a circle is constantly accelerating according to Newton, and the acceleration of the can creates a inertial effect pulling at you. That way we don't have to define a inertial frame for it?
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Re: Is centrifugal force false?

Postby SolarFluxUnit on July 27th, 2011, 12:58 pm 

gsalih wrote:Because if one swings a can in a circle
and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.


You see, the can travels tangent to the circle because the force you swing it with is a vector (changes direction in every moment of circulation ofcourse) and because of that force.
It has absolutely nothing to do with centrifugal force because centrifugal force is always neutralised by centripetal force (you know, the centrifugal force pulls out, centripetal in).

As for the very existance of these two forces, they are imaginary; made up to explain, for example, water not spilling out of the bucket when rotating it.
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Re: Is centrifugal force false?

Postby CanadysPeak on July 27th, 2011, 3:13 pm 

SolarFluxUnit wrote:
gsalih wrote:Because if one swings a can in a circle
and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.


You see, the can travels tangent to the circle because the force you swing it with is a vector (changes direction in every moment of circulation ofcourse) and because of that force.
It has absolutely nothing to do with centrifugal force because centrifugal force is always neutralised by centripetal force (you know, the centrifugal force pulls out, centripetal in).

As for the very existance of these two forces, they are imaginary; made up to explain, for example, water not spilling out of the bucket when rotating it.


Centripetal force is a "real" force. You can see this if you find a really stiff spring scale and use that to swing the bucket. The faster you swing the bucket, the higher force (weight) reading you'll get on the spring scale. If you can't find a spring scale, use something like 10 pound fishing line (which breaks somewhere between 10 and 25 pounds). Swing the bucket fast enough (No! Out in the yard - it's gonna spill when the string breaks) and you'll see the string break, indicating you exceeded that breaking force.
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Re: Is centrifugal force false?

Postby SolarFluxUnit on July 27th, 2011, 5:11 pm 

Oh right, sorry, I kind of limited myself to planetary circulation here (when talking about centrifugal/centripetal force) where they actually do neutralise themselves...it's just more in my field of interest so....
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Re: Is centrifugal force false?

Postby Greek_Geek on September 11th, 2011, 12:33 am 

Depends on your definition of a force. Some fundamentalist physicist would define a force as being the big 4 (Electromagnetic, gravity, strong, weak). Other physicists apply the word force to other things, such as the "normal" force, which is just the natural resistance of any material. Even friction can be thought of as a force. In the end however, these "smaller" forces are just the collected influence of the big 4.

If that doesn't help, think of it as this way. You can say that a force is anything that changes and objects velocity, true? Velocity is speed with a vector. It is implied that changing velocity means changing speed, but based on its actual definition, changing the direction of a moving object still means changing its velocity. So an object experiencing centrifugal force is an object not changing in speed but in its direction of motion.
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Re: Is centrifugal force false?

Postby Larry-the-lemur on October 6th, 2011, 9:54 am 

My guess is that there are 2 forces at wok here: the centrifugal force that propels the can outwards and the kinetic force that propels it in the same direction of the swing.

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Re: Is centrifugal force false?

Postby Larry1957 on November 9th, 2011, 3:30 pm 

I'd like to share my thoughts on centrifugal force if I may though a short video I produced in that regard. Feedback would be appreciated.

http://s1020.photobucket.com/albums/af323/LarryWagner1234/?action=view&current=CentrifugalForceexplaination.mp4

Larry
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Re: Is centrifugal force false?

Postby CanadysPeak on November 9th, 2011, 7:04 pm 

Larry1957 wrote:I'd like to share my thoughts on centrifugal force if I may though a short video I produced in that regard. Feedback would be appreciated.

http://s1020.photobucket.com/albums/af3 ... nation.mp4

Larry


You're using the term "centrifugal force" to describe things that are already well-described by other terms. You would do well to look at conventional Physics and learn the definitions there.
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Re: Is centrifugal force false?

Postby Larry1957 on November 17th, 2011, 11:34 am 

I think my understanding of centrifugal force may be unique. It was recently questioned, so I made a short video to make my thoughts clear on it.

http://s1020.photobucket.com/albums/af3 ... tion-1.mp4

Feedback on it would be appreciated.

Larry
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Re: Is centrifugal force false?

Postby genemachine on December 20th, 2011, 9:11 pm 

This is my attempt to explain centrifugal force..

In the absence of any force an object will travel in a straight line.

To make an object travel in a circular path, a force of just the right size needs to accelerate it towards the centre.

To calculate the size of the force required to maintain a circular orbit it is convenient to pretend that it is opposed by a "centrifugal" force of equal magnitude and opposite direction. The magnitude of this centrifugal force is m*v^2/r where m=mass, v=velocity, and r=radius.

If the centrifugal force actually existed we would not have a circular orbit, we would have a straight line trajectory. It is merely a convenience to pretend that we have this force when calculating the force needed to maintain a circular orbit.
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